This invention relates to a boiler having an outer wall of weldable material and spaced therefrom is an inner chamber wherein a heat exchange of gaseous media takes place at temperatures higher than the permissible operating temperature of the outer boiler wall. More particularly, the present invention relates to a construction and arrangement of parts to supply and discharge gaseous media for the inner chamber through the outer wall of such a boiler.
A boiler of this type is employed to transfer thermal energy by using a gaseous medium. The origin of thermal energy is the heat originating mainly from nuclear energy and conveyed through the medium of a noble gas. The temperatures to which the noble gas is heated by the nuclear energy are above the acceptable temperature, i.e., working temperature, for the weldable material forming the outer boiler wall. The boiler is conventionally constructed as a double-jacket unit to receive a flow of hot cooling gases from a nuclear reactor. In the boiler, the hot cooling gas flows around a reactor or heat exchanger situated within an inner boiler from where the gas flows upwardly through a cooler wherein, for example, steam is generated. While the hot cooling gas fed to the boiler has an entry temperature of about 950.degree. C., the temperature of the gas drops below 400.degree. C., e.g., to 250.degree. C., after passing from the cooler. The cooler used to generate steam within the inner boiler is opened at its top so that the cooled noble gas can flow into an annular chamber located between the heat exchangers in the inner boiler and the outer boiler wall. A blower communicates with the annular chamber in the boiler at this point. In this way, the outer jacket of the boiler can be designed for passage of a noble gas at a lower temperature of, for example, 250.degree. C. The usual or conventional operating pressure of the noble gas in the boiler is 50 bar.
A particular problem occurs in such a boiler where the conduit line leading to the inner boiler chamber for supplying and discharging gaseous media thereto must pass through the outer boiler wall which consists of weldable material. It is impossible to weld the conduit lines directly to the boiler wall because the required strength cannot be obtained since the boiler wall thickness is increased at this point to provide the required thermal conductivity. The conduit line has already been constructed in the form of a double-jacket tube assembly and the annular space between the tubes has been filled with thermally-insulating material. The layer of insulating material must be relatively thick, thus requiring an outer tube with a large diameter and in most cases additional reinforcement of the boiler wall is required. This is because there is a very large difference between the temperature of the gaseous media supplied and discharged by the pipes passing through the boiler wall and the acceptable operating temperature for the material forming the outer boiler wall. Moreover, a very large number of conduit lines is required to pass through a plane about the circumference of the boiler when cooling gases flow from a nuclear reactor into heat exchangers or reactors in a boiler. The number of required conduit lines is so great that the required pipe couplings, etc. connected thereto in a circumferential plane externally of the boiler contact one another even when the couplings are arranged in a staggered manner.